Method and apparatus using enhanced attachment for improved connectivity in telecommunications

ABSTRACT

Voice services provided over a packet switched facility such as a Frame Relay network are enhanced with routing capability by providing for attachment devices which, on initialization with the network, attempt to discover other similar attachment devices on the network. Thereafter the attachment devices exchange information on terminal accessibility to improve connectivity over the network.

TECHNICAL FIELD

[0001] The invention relates to telecommunications and more particularlyto improvements in digital provisioning for voice services.

BACKGROUND OF INVENTION

[0002] For the majority of the history of telecommunications, voice hasbeen the predominant application. Indeed, only recently has datatransmission become significant. Nevertheless, the advances that havebeen made in data communications have been so profound that it is notunusual for modern data communications technology to be applied tocarrying voice, in addition to data.

[0003] Many of the improvements in data communications relate to packetswitching. Different varieties of data communication technology fallingunder the class of packet switching include Frame Relay (hereinafteralso FR), Asynchronous Transfer Mode (ATM), Internet Protocol (IP),voice over Internet Protocol, SMDS, cell relay networks or the like.

[0004] Packet switching networks provide a payload transport capabilitywhich is applied to voice communication purposes. However, packetswitching networks lack other services which are typically found in thevoice dedicated network. For example, the routing or addressingfacilities typically found in a voice network are not present in apacket switching network and accordingly, in order to provide packetswitched transport capability for voice, some accommodation must be madefor routing calls.

[0005] More particularly, when a voice switch such as a Private BranchExchange (PBX) is adapted for service over the Integrated ServicesDigital Network (ISDN) addressing information is carried in the socalled D channel. When adapting a PBX to connect to a Frame Relay (FR)network, the D channel, sourced at the PBX, terminates at an attachmentdevice or more particularly, a Frame Relay Attachment Device (FRAD).

[0006] In this configuration, the FRAD is designed to provide a routingservice to the PBX. The FRAD is capable of directing the call setupmessage to a particular Permanent Virtual Circuit (PVC) in the FRnetwork so as to access the called terminal. In order to provide thisservice, however, the FRAD needs a correlation between terminal address(in voice applications this is the same as a telephone number orextension) and FR network channel. One of the difficulties with carryingvoice services over packet switched networks is the problem of providingthe FRAD or the like with this information. Complicating the problem isthe dynamic nature of the information, requiring it to be constantlyupdated and/or revised so that it is accurate.

SUMMARY OF INVENTION

[0007] The invention solves the foregoing problem and provides technicaladvantages as described below. In particular, with respect to oneaspect, the invention provides a method of enhancing the provision ofvoice services via packet switched facilities in which a voice switch isconnected to the packet switched facilities using an associatedattachment device, the method including:

[0008] storing, in plural attachment devices, information respectingvoice terminals accessible through the associated voice switch;

[0009] generating a request from a particular attachment device toanother attachment device for information respecting voice terminalsaccessible via the another attachment device's associated voice switch;and

[0010] storing at the particular attachment device information receivedin response to the request.

[0011] With respect to another aspect, the invention relates to a systemfor providing enhanced voice services via packet switched facilitiesincluding a voice switch connecting to the packet switched facilitieswith an associated attachment device, the system including:

[0012] means in plural attachment devices for storing informationrespecting voice terminals accessible through the associated voiceswitch;

[0013] means in plural attachment devices for generating a request toanother attachment device for information respecting voice terminalsaccessible via the another attachment device's associated voice switch;and

[0014] second storing means in plural attachment devices for storinginformation received in response to the request.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will now be described in further detail inthe following portions of this specification when taken in conjunctionwith the attached drawings in which like reference characters identifyidentical apparatus and in which:

[0016]FIG. 1 is a block diagram illustrating a system operating inaccordance with the present invention;

[0017]FIGS. 2A through 2C are flow charts which represent the operationof typical attachment devices of FIG. 1;

[0018]FIG. 3 illustrates information which may be found in the memory ofan attachment device in accordance with the present invention;

[0019]FIG. 4 illustrates a correlation of several PVCs and attachmentdevices;

[0020]FIGS. 5A and 5B relate to an embodiment of the invention in anapplication in which Switched Virtual Channels are used and, inparticular, FIG. 5A shows a portion of an initialization routine for atypical FRAD and FIG. 5B shows the relationship between exemplary FRADs310, 311 and 312 and the FR 300;

[0021]FIG. 6 illustrates an application of the invention which allowscooperation among attachment devices in multiple frame relay networks solong as they have gateway access to each other; and

[0022]FIG. 7 illustrates portions of the data in the “own” terminallisting of particular FRAD entities of FIG. 6.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION

[0023]FIG. 1 shows a frame relay network 100. Included in the framerelay network 100 and not specifically illustrated in FIG. 1 are aplurality of data sources and sinks (here the term data is used todistinguish the form of the information from voice). FIG. 1 also showsseveral PBXs 201-203 which employ the services of the frame relaynetwork to transmit voice. Coupled between each voice switch PBX 201-203and the frame relay network 100 is an associated attachment device,particularly a Frame Relay Attachment Device (FRAD) such as FRADs301-303.

[0024]FIG. 1 also shows the connection of each PBX to the local PublicSwitched Telephone Network or PSTN (local PSTN refers to the portion ofthe PSTN which is accessible to the associated PBX without incurringtoll charges). Particularly, each PBX (including each of the illustratedPBX's 201-203) is capable of dialing into the local PSTN network andreaching thousands of telephone terminals. Because of typical callingtariffs, there is no per call charge for accessing any of this largenumber of terminals. More particularly PBX 201 may access any terminalconnected in the local PSTN 401. Likewise, PBX 203 can access anyterminal connected in the local PSTN 403. In addition, of course, manytelephone terminals, such as terminal T1 or T5 can access many otherterminals, such as terminals T2. If this access traverses a toll network500, that access will carry a toll charge. However, if such an accesscan be made through the Frame Relay network 100 then the toll charge canbe avoided. FIG. 1 shows specific terminals connected in different localPSTNs; terminal T5 is connected in local PSTN 401 and terminal T2 isconnected in local PSTN 403. Terminal T1 is also connected in local PSTN401 via PBX 201.

[0025] Typically, a PBX may be configured to use ISDN. As such, when acall is placed by a terminal, such as the terminal Ti, the PBX 201formulates a call setup message in the D channel. The call setup messageis received by the associated attachment device 301. The associatedattachment device 301 reads the dialed number, i.e. the identificationof the called terminal, such as the terminal T2, and forwards a callsetup message across the FR 100 to the FRAD 303 which is associated withthe PBX 203.

[0026] In order to be able to perform these functions, the FRAD 301 must“know” that the called terminal T2 is attached to the PBX 203 which isassociated with the FRAD 303. More succinctly, the FRAD 301 must “know”that the call is intended for the voice switch associated with the FRAD303.

[0027] One way to provide the FRAD 301 with this information is tomanually insert the information into FRAD 301. This requires the manualloading of data in each of a plurality of attachment devices, which dataidentifies the terminals associated with each of the other attachmentdevices. Even if this were not a daunting task, changes in this datawould quickly render the effort of little or no value.

[0028] To ease the burden and enhance the provision of voice servicesover the packet switched facility the attachment devices are modified tocooperate in sharing information respecting terminal accessibility. Moreparticularly, and referring to FIG. 1, FRAD 301 is supplied withinformation identifying the telephone terminals which are accessible tothe associated PBX, e.g. PBX 201. Accessible, in this context, meansaccessible without toll charges and without relying on FR 100. In otherwords, FRAD 301 is supplied with and stores information identifying thetelephone terminals associated with the local PSTN 401. Each of theseterminals is a terminal which is accessible to the PBX 201 withoutincurring toll charges. Each other attachment device, such as FRAD 302,FRAD 303, etc., is also supplied with this information, i.e. informationidentifying telephone terminals accessible through the associated PBXwithout incurring toll charges. In this fashion, FRAD 302 obtainsinformation identifying telephone terminals accessible to PBX 202, andFRAD 303 obtains information respecting telephone terminals accessiblevia PBX 203, etc. The manner in which this class of information issupplied to the attachment devices may be manual or via any othersuitable procedure.

[0029] Thereafter, the attachment devices exchange information with oneanother. In this way, for example, FRAD 301 obtains the information thatidentifies the telephone terminals accessible via the PBX associatedwith the attachment device 302 and the telephone terminals accessiblevia the PBX associated with attachment device 303, etc.

[0030] With this information, when the call setup message is received bythe attachment device 301, for example, it can determine, by reviewingthis information, if the called terminal is among the list of terminalsaccessible to any PBX coupled to the attachment devices of frame relaynetwork 100. Upon learning that the called terminal is accessible to anidentified one of the PBXs coupled to the frame relay network 100, thecall setup message is directed to the attachment device associated withthat PBX, as is described in more detail below.

[0031] More particularly, frame relay networks include Permanent VirtualCircuits (PVC) and may also include Switched Virtual Circuits (SVC). Thesimpler frame relay networks, including most frame relay networksimplemented today, are supplied with PVC to the exclusion of SVC. Interms of FIG. 1, then, PBX 202/FRAD 302 is accessed from FRAD 301 via aparticular PVC, in other words one PVC, available at FRAD 301, isdedicated to reaching FRAD 302. A different PVC, available at FRAD 301,is used by FRAD 301 to access FRAD 303.

[0032]FIG. 4 represents the function of six PVCs in frame relay network100. In particular, PVC A is available at attachment device 301 and itaccesses attachment device 302. PVC B is also available at attachmentdevice 301 and it accesses device 303, etc.

[0033]FIG. 3 illustrates a portion of the memory of a typical attachmentdevice such as FRAD 301. The memory illustrated in FIG. 3 is dedicatedto storing information respecting terminals which are accessible eitherdirectly or via FR100. The information is divided into two portions, afirst portion is shown at the left, headed “OWN”. This informationidentifies the telephone terminals accessible to the particularattachment device via the associated PBX. If, for example, the PBX 201were located in Washington, D.C., this complement of terminals would beidentified (in conventional NPA or NPA-NXX fashion) as shown in FIG. 3.In particular, the PBX in Washington, D.C. is capable of accessing anytelephone terminal with a 202 NPA. In addition, there is a range oftelephone terminals with a 703 prefix which are accessible to the PBX inWashington, D.C. This is identified in FIG. 3 as 703-XXX through703-YYY. Likewise, there is a range of telephone terminals with a 301NPA which are accessible to the PBX in Washington, D.C. These areidentified in FIG. 3 as 301-XXX through 301-ZZZ. The list just describedidentifies each telephone terminal accessible to the PBX 201 on theassumption that that PBX was located somewhere in Washington, D.C.

[0034] Prior to interaction between a particular attachment device suchas the FRAD 301 and any other attachment device, the information justdescribed is the only information available to that particularattachment device respecting telephone terminals accessible to theassociated PBX.

[0035] After the attachment device 301 is placed into service andallowed to interact with other attachment devices as will be described,its memory will contain additional information, i.e. that information inFIG. 3, shown at the right. This information is divided into twoexemplary portions, each identified by a different PVC identification.For example, FIG. 3 shows a first PVC, i.e. PVC A, and a second PVC,i.e. PVC C. Each portion of FIG. 3 also associates a list of accessibletelephone terminals. Under the heading PVC A, FIG. 3 shows two groups oftelephone terminals, one including a particular NPA, in this case NPA1,as well as some but not all of telephone terminals with a different NPA,i.e. NPA2. In particular, telephone terminals in the range NPA2-XXXthrough NPA2-ZZZ are included. FIG. 3 also indicates that PVC C isassociated with a different complement of telephone terminals, sometelephone terminals including an NPA3 prefix, and particularly NPA3-XXXthrough NPA3-ZZZ as well as all telephone terminals with an NPA4 prefix.

[0036] The manner in which this information is acquired and the mannerin which it is used will now be described.

[0037]FIGS. 2A through 2C show respectively an initialization processimplemented by a typical attachment device, a receive query process anda change in terminal data process, all executed by an attachment deviceat different times. The initialization process is executed on theattachment device joining a particular network. In order to explain theoperation of this process, assume that the system shown in FIG. 1 hasbeen in operation for some time. In particular, the frame relay network100 has coupled to it attachment devices 302 and 303, each of which inturn is associated with its respective PBX, PBX 202 and PBX 203. Inaddition, each of the attachment devices 302 and 303 has informationrespecting terminals accessible through its associated PBX as well asinformation respecting terminals accessible through the other (themanner in which the latter function is accomplished will be describedbelow). Furthermore, assume that FRAD 301 has just been initialized inthe frame relay network 100. As part of that initialization process,steps 221 through 227 are performed.

[0038] Step 221 generates a query from the attachment device 301 tolocate other attachment devices connected to the frame relay network100. Two such attachment devices which will be located are attachmentdevices 302 and 303. Assume, for example, that at step 222, attachmentdevice 302 is located. Thereafter, step 224 generates a query, directedat the attachment device 302, for terminal data. The query is directedat attachment device 302 by being directed to the particular PVC whichallows attachment device 301 to access attachment device 302. The queryfor terminal data is a query for the data of attachment device 302stored in its own terminal portion, i.e. the left hand portion of FIG.3. As will be described below, when attachment device 302 receives thisquery, it returns the requested data such that at step 225, attachmentdevice 301 records the received data along with the PVC ID. This data isrecorded as a block in the right hand portion of the memory ofattachment device 301. Thereafter, step 226 sends own terminal data fromthe attachment device 301 to the attachment device 302. Step 227 thendetermines whether additional PVCs should be queried to locateadditional attachment devices. If the positive response is active, thenstep 223 selects another PVC and the process is repeated. In thisfashion, attachment device 301 will attempt to locate an attachmentdevice on each PVC available to it. Each time another attachment deviceis located, the attachment devices will exchange terminal data, i.e.each will send the other its own terminal data information.

[0039]FIG. 2B illustrates the operation at an attachment device when itreceives a query for own terminal data. The first step, step 230,identifies the PVC on which the query has been received. Thisinformation allows the receiving device to reply to the device whichinitiated the query. Step 231 sends own terminal data, as requested, andstep 232 records the received data (that is, the data received from thequerying attachment device) along with the PVC ID.

[0040] Finally, assuming that all attachment devices have exchanged ownterminal data with all other attachment devices, and that no newattachment devices enter the network 100, there still is a requirementto cover changes in accessible terminal information because of outsidefactors, e.g. new NPAs, etc. Accordingly, the process of FIG. 2C isimplemented when a change in own terminal data is identified at aparticular attachment device. In particular, once a change in ownterminal data has been detected, the attachment device must exchangethat information with each other attachment device which is within theframe relay network 100. Function 240 is used to select a PVC associatedwith an attachment device, i.e. the PVC is identified in the first lineon the blocks in the right hand portion of FIG. 3. Functions 241 through243 generate a query for own terminal data of the another attachmentdevice located at the selected PVC. Function 242 records the receiveddata and the PVC ID and function 243 sends the now-changed own terminaldata. Function 244 is used to determine when all pertinent PVCs havebeen run through the process of functions 240 through 243.

[0041] The manner in which the information in the attachment devicememory is used should be apparent from FIG. 3 but a brief descriptionwill suffice. In particular, assume that a call is generated at PBX 201for a particular called number which is included in NPA3. PBX 201incorporates this call setup message into the D channel and transfers itto attachment device 301. Attachment device 301 reviews the list oftelephone terminals identified in memory (see the right hand portion ofFIG. 3). In the first block (under the heading PVC A), the attachmentdevice would not find the called terminal since this block includes onlyNPA1 and NPA2. However, when the attachment device 301 checks the nextblock, it will find that it includes NPA3 terminals and assuming thatthere is a match between the called number and the range of NPA3 numbersaccessible, then the attachment device 301 will send the setup messagefor this particular call through PVC C to access the appropriateattachment device for call completion.

[0042] The foregoing description is based on a frame relay network whichemploys PVC and not SVC. FIG. 4 for example shows that the six PVCsillustrated are dedicated so that, for example, PVC A only accessesdevice 302 from device 301.

[0043] The invention is also applicable, however, to networks whichinclude SVC. The invention operates with even more capability in the SVCenvironment than in the PVC environment.

[0044] In the PVC environment, for every attachment device pair whichdoes not have a PVC therebetween, there are some terminals that cannotbe reached; in other words, complete connectivity requires a full mesh.The SVC capability eliminates the necessity for fully meshedconnectivity.

[0045] The SVC allows a given channel to be addressed, i.e. to accessmore than one destination as opposed to the PVC which is dedicated to asingle destination. Thus, a typical FRAD can use a channel into the FRto connect to any other FRAD which is also part of the FR, so long asthe address of the other FRAD is known.

[0046] Refer to FIG. 5B. FIG. 5B illustrates a frame relay network 300which includes, among other things, Switched Virtual Channel capabilityand includes FRAD 310-312. We will assume for this description that FRAD310 has been denominated as the master or the controller. We will alsoassume that newly added FRAD 311 is in the process of being initialized,whereas FRAD 312 has been initialized at some time in the past. In theinitialization process for FRAD 311, FRAD 311 will receive informationidentifying FRAD 310, and its address, as the network controller. Ratherthan having to query each possible address from FRAD 311, FRAD 311 thenmerely accesses FRAD 310, using the address already supplied. Thus, withSVC capability in the frame relay network, initialization steps formerlyshown in FIG. 2A can be replaced by the steps shown in FIG. 5A. Function230 generates the query to the master FRAD as already explained. Thatquery requests the addresses for all other FRADs, function 231. Thequerying FRAD, 311 in this case, stores the addresses, function 231, andthen initializes its address register, function 232. The initializingFRAD 311 will then perform functions 233-235 for each address it hasreceived. These functions provide for the exchange of local terminalinformation between the new FRAD and the “old” FRAD. Functions 236 and237 provide for changing the address register to reach other, yetunprocessed, FRADs, until all members of the network have beenprocessed, at which time the process terminates.

[0047] At the time FRAD 311 receives address information on otherattachment devices in the network from the master FRAD 310, the addressdata base of master FRAD 310 is altered by adding information respectingthe new addition, FRAD 311. Accordingly when a further new attachmentdevice joins the network it will receive addressing information onattachment device 311 along with the others previously in the network.

[0048] The foregoing embodiments, including frame relay networks withonly PVC and frame relay networks with SVC, are limited to singledomains, i.e. there is only a single frame relay network. The invention,however, is not limited to single domain applications as will now bedescribed.

[0049]FIG. 6 shows two domains, one centered on frame relay network 600and the other centered on frame relay network 700. Each domain can beenhanced with the features of the present invention. However, in thismultiple domain application further advantages accrue. Application ofthe invention allows any terminal in local PSTN 801 to connect via framerelay network 600 to any terminal in local PSTN 802 or 803, as hasalready been explained. Likewise, employing the principles of theinvention, any terminal in exemplary local PSTN 806 can connect to anyterminal in local PSTN 805 or 802. However, since local PSTN 802 iscommon to the two domains, the FRADs 604 and 602 can act as “gateways”into its local domain for the remote domain, as will now be explained.

[0050]FIG. 7 shows the internal memories for FRAD 604 and FRAD 602,respectively and particularly that portion in which the own terminalinformation is identified. In this example, we have assumed that localPSTN 802 (which is local to FRAD 604 and FRAD 602) represents theWashington, D.C. area such that the own terminal identification for FRAD602 and 604 is the same as that used for FIG. 3. Thus the own terminalfor both FRAD 604 and 602 identify the following, as local terminals:

[0051]202

[0052]703-xxx-yyy

[0053]301-aaa-bbb

[0054] However, in its function as a gateway FRAD 604 also identifies,following a domain mark (to indicate that the terminals listed below arein a different domain), information including NPA information for localPSTN 801 and local PSTN 803. In other words, when FRAD 604's “own”terminal information is dispersed to FRAD 606 and 605 via FR 700, thoseentities will discover that they can reach local areas 801 and 803 viaFRAD 604. Correspondingly, the own terminal list contained in FRAD 602will include, in addition to the 202, 703 and 301 NPA information, andset off by a domain mark, the NPA information for local PSTN 806 and805. Thus when FRAD 602 “own” terminal information is dispersed amongthe members of FR 600, those members (including FRAD 601 and 603) willlearn that they can reach PSTN 806 and 805 via FRAD 602 as a “gateway”.

[0055] In operation, the presence of the data below the domain mark inthe memory of FRAD 602 will result in the distribution of thatinformation to other members of FR 600. Distributing that information toFRAD 601 and 603 (other members of FR 600) will enable those devices torecognize that terminals in local PSTN 805 and 806 are accessible in the“other domain”. Likewise, the presence of the data below the domain markin the memory of FRAD 604 will result in the distribution of thatinformation to other members of FR 700. Distributing that information toFRAD 605 and 606 (other members of FR 700) will enable those devices torecognize that terminals in local PSTN 801 and 803 are accessible in the“other domain”.

[0056] While several embodiments of the invention have been described indetail, those examples should not be considered limiting, rather thescope of the invention should be construed in accordance with the claimsattached hereto.

What is claimed is:
 1. A method of enhancing the provision of voiceservices via packet switched facilities in which a voice switch isconnected to the packet switched facilities using an associatedattachment device, the method including: storing, in plural attachmentdevices, information respecting voice terminals accessible through theassociated voice switch, generating a request from a particularattachment device to another attachment device for informationrespecting voice terminals accessible via the another attachmentdevice's associated voice switch, and storing at the particularattachment device information received in response to the request fromthe particular attachment device.
 2. The method of claim 1 wherein theparticular attachment device, prior to generating a request to anotherattachment device, generates a query to one or more virtual circuits,accessible from the particular attachment device, to determine if thechannel accesses another attachment device, and generates the request inan instance in which another attachment device is identified.
 3. Themethod of claim 1 or claim 2 wherein the particular attachment device,transmits accessibility information, respecting voice terminalsaccessible through the voice switch associated with the particularattachment device, to the another attachment device.
 4. The method ofclaim 1 or claim 2 wherein the another attachment device responds to therequest by the particular attachment device by transmitting theaccessibility information respecting voice terminals reachable via theassociated voice switch.
 5. The method of claim 2 in which theparticular attachment device stores, along with the informationrespecting voice terminals accessible through the another attachmentdevice's associated voice switch, information identifying the particularcircuit through which the another attachment device is accessible. 6.The method of claim 2 wherein the act of generating a query is executedon initialization of the particular attachment device.
 7. The method ofclaim 4 or 5 which further includes exchanging identities of voiceterminals accessible through the associated voice switch with otherattachment devices when there is a change in the set of voice terminalsaccessible through the associated voice switch.
 8. The method of claim 1or claim 2 in which the attachment device is a frame relay attachmentdevice and the packet switched facility is a frame relay network.
 9. Themethod of claim 1 or 2 in which the voice switch is a PBX and is alsocoupled to the PSTN.
 10. The method of claim 1 wherein the informationrespecting voice terminals accessible through the associated voiceswitch identifies terminals which are directly accessible to theassociated voice switch or terminals which are accessible through theassociated voice switch through a packet switched network.
 11. A systemfor providing enhanced voice services via packet switched facilitiesincluding a voice switch connecting to the packet switched facilitieswith an associated attachment device, said system including: means inplural attachment devices for storing information respecting voiceterminals accessible through the associated voice switch, means in aparticular attachment device for generating a request to anotherattachment device for information respecting voice terminals accessiblevia the another attachment device's associated voice switch, and secondstoring means in the particular attachment device for storinginformation received in response to the request.
 12. The system asrecited in claim 11 which further includes: means in plural attachmentdevices for generating a query to one or more virtual circuits,accessible from an attachment device, to determine if the circuitaccesses another attachment device, and wherein said means in aparticular attachment device for generating a request, generates therequest in an instance in which another attachment device is identifiedat a particular circuit.
 13. The system of claim 12 wherein theparticular attachment device further includes transmit means fortransmitting accessibility information, respecting voice terminalsaccessible through the voice switch associated with the particularattachment device, to another attachment device after identifying theanother attachment device.
 14. The system of claim 13 wherein theattachment device includes means to respond to the request bytransmitting the accessibility information respecting voice terminalsaccessible via the associated voice switch.
 15. The system of claim 13in which the means for storing stores, along with the informationrespecting voice terminals accessible through the attachment device'sassociated voice switch, information identifying the particular circuitthrough which the another attachment device is accessible.
 16. Thesystem of claim 12 or claim 13 wherein the means for generating a queryis operated in response to initialization of the associated attachmentdevice.
 17. The system of claim 11 where plural attachment devicesfurther include means, responsive to a change in the set of voiceterminals accessible through the associated voice switch, for initiatingan exchange of identities of voice terminals accessible through theassociated voice switch with other attachment devices.
 18. The system ofclaim 11 in which the attachment device is a frame relay attachmentdevice and the packet switched facility is a frame relay network. 19.The system of claim 11 which the voice switch is a PBX and is alsocoupled to the PSTN.
 20. The system of claim 11 wherein the informationrespecting voice terminals accessible through the associated voiceswitch identifies terminals which are directly accessible to theassociated voice switch or terminals which are accessible through theassociated voice switch through a packet switched network.